<div id="app">
  <h1>{{ title }}</h1>
  <p>{{ reverseTitle }}</p>
</div>
<script src="https://unpkg.com/vue@3"></script>
<script>
  const { createApp } = Vue
  createApp({
    data() {
      return {
        title: 'title'
      }
    },
    computed: {
      reverseTitle() {
        return this.title.split('').reverse().join('')
      }
    },
    watch: {
      title() {
        console.log('title change');
      }
    },
    mounted() {
      setTimeout(() => {
        this.title = this.title.split('').reverse().join('')
      }, 1000)
    },
  }).mount('#app')
</script>